Two issues concerning lipomas continue to provoke debates among paediatric neurosurgeons : one is whether asymptomatic lipomas should be treated with prophylactical surgery; the other is with what surgery.

Regarding the first issue, arguments continue unabated between the “cutters” (those who advocate early resection) and the “non-cutters” (those who would do surgery only after symptoms appear), but one thing is beyond dispute : spinal cord lipoma is a progressive disease. In 2004, Kulkarni et al. [27], from L’Hopital Necker-Enfants Malades, Paris, published a prospective study of a relatively large cohort of children with lipomas that were followed without surgery and concluded that asymptomatic lipomas have a 33% chance of deterioration over 9 years. A comparable though retrospective study from London in 2012 [73] similarly reported a 40% 10 year deterioration rate in unoperated asymptomatic lipomas. The London study also showed that females with transitional lipomas and/or a terminal syrinx fared even worse. Thus, since half of their cohort were females and approximately 70% of their lipomas were of the transitional type, the poor outcome rate of the group, when projected to a larger cohort size and longer follow-up, may well exceed 40%. Such dire statistics for untreated lipomas in children with presumably long actuarial survival seem to demand some type of intervention. Ironically, the Parisian group advised against prophylactic surgery because their own results of prophylactic partial resection in a later report showed an even higher probability of late deterioration than the group with no surgery [27,63]. The logical conclusion, considering the high progression rates of both the natural disease and partial resection, is that asymptomatic lipomas do indeed need surgery, just not partial resection.

Which brings in the second issue of what might be the most effective surgery that offers long term benefits over the natural history of complex lipomas. Historically, the traditional technique had always been partial resection [1,6,19,22,29,40,70], but despite its wide usage, data from most large series do not show that it offers adequate long-term protection against disease progression. For example, Dorward et al. [16] reported a symptomatic recurrence rate of 48% over merely 2.2 years. Colak et al. [11] reported a 52% recurrence rate over 10 years with partial resection, but their series comprised 37% terminal lipomas, which are known to have much better prognosis than dorsal and transitional lipomas, implying that the progression rate if calculated just for the latter lipoma types must be even higher than 52%. Pierre-Kahn et al. [62] documented a 10 years recurrence of 46% but again their series contains many terminal and filar lipomas; and Cochrane et al. [10] and Xenos et al. [74] similarly recorded early recurrence. These disturbing results pose the obvious question whether leaving behind a large amount of residual fat with its broad, raw, and sticky abraded surface actually provokes new adhesions to the adjacent dura and consequently incurs earlier and firmer retethering than if the lipoma had been left untouched. Or alternatively, whether complete removal of the bulky lipoma plus measures to render the now pliant neural placode less “sticky”, would impart greater permanent benefits than partial resection.

The need for a different procedure other than partial resection occurred to me in 1991, when my own series of 116 partial resections following conventional teaching [4,19,40,41,62,67,70] (we were taught always to leave a goodly layer of fat on the neural placode and that exposing even a glimmer of cord tissue through the fat was a sin) showed an alarming 65% symptomatic recurrence rate over 11 years. This untenable situation compelled me to entertain the then iconoclastic concept of complete resection of the lipoma, strategic reconstruction of the neural placode, and expansile duraplasty. My rationale for this more aggressive approach [59] is founded on three hypotheses : 1) the high recurrence rate after partial resection is due to re-tethering at the resection site; 2) re-tethering is in turn promoted by three conditions : a tight content-container relationship between the affected placode and its adjacent intradural space, a broad “sticky” slab of remaining fat, and incomplete separation of the terminal placode from the caudal fat (see below); and 3) total resection eliminates these conditions contributory to re-tethering, and thus reduces the probability of late deterioration. The object of this proposed new operation is therefore to create a milieu least conducive to re-sticking of the neural placode. The first premiss towards this goal is predicated on the observation that the spinal cord normally shows considerable intradural motion to gravity and postural changes demonstrable on dynamic imaging [5,15]. Lowering the content-container ratio and amplifying the amount of free placode movements within the dural sac should therefore reduce sustained contacts between placode and dura, hence also the probability of adhesion. To achieve this in a “virgin” (previously unoperated) lipoma, the bulk of the lipoma-cord composite must first be severely trimmed by resecting all or most of the engorging fat down to the thin, supple neural placode; for “redo” lesions that have had previous surgery, the stiff fibrous scar must also be removed. The goal is to render the thinnest, most malleable neural placode so that through tensionless pia-to-pia neurulation (see below), a slender but unstrangled, pia-covered neural tube can be created. The sticky lipoma bed is thus concealed within this tube, and the dural sac is then made capacious by a generous graft. Finally, total elimination of the obscuring fat will also enhance the chances of terminal untethering.

In 2009 and 2010 [59,60], my colleagues and I published our early series of 238 patients who had total/near-total resection of complex lipomas and compared their short and long term outcomes with our prior series of 116 patients with partial resection. In 2013, we updated our series of total resection to 315 cases [60], and recently, our number has risen to over 450 cases [53,55]. Our ever enlarging data pool unfailingly shows an overwhelming advantage of total over partial resection in almost all respects, but the subset of asymptomatic virgin lipomas continues to pique uncertainties and controversies among some paediatric neurosurgeons. This review therefore re-examines three recurring questions : 1) is total resection better than partial resection for both symptomatic and asymptomatic lipomas?; 2) is total resection better than no surgery for asymptomatic lipomas, i.e., should they all be treated prophylactically with total resection?; and 3) is partial resection worse than no surgery and, if so, should it be strongly discouraged?

There is an increasing body of literature proposing newer and newer nomenclatures and classifications of spinal cord lipomas but they are essentially variations of the same existing scheme. Here, we are sticking to our old classification, solidly based on embryogenesis, as follows.

An understanding of the embryogenesis of lipomas is helpful in appreciating the surgical nuances.

Intraoperative electrophysiological monitoring is sine qua non in lipoma surgery [49,50,56,59,61].

The surgical technique described below concerns the case of an unusually large and rambling dorsal lipoma, that illustrates most of the key technical points of total resection applicable to both dorsal and transitional lipomas. The case is a 12 months old girl who was neurologically normal at birth but had magnetic resonance imaging (MRI) because of a lumbosacral fatty lump, which showed a moderate-sized dorsal lipoma involving the lower lumbar cord above a normal looking conus. At 1 year, she began showing left leg weakness and repeat MRI showed massive enlargement of the lipoma (Fig. 9).

The author’s data show that total or near-total resection of spinal cord lipomas can be achieved in over 90% of cases [59-61] (Fig. 34). In cases where small bits of fat were left on the DREZ for fear of gouging, they have been wrapped up within the neurulation folds “out of mischief” (Fig. 35). In 8% of patients, the residual fat represents the ventral component of a chaotic lipoma that had been intentionally left untouched and piacovered and presumably harmless.

To estimate the “looseness” or degree of freedom of the reconstructed placode within the expanded CSF space, we invented the cord-sac ratio, defined as the ratio of the diameter of the bulkiest portion of the reconstructed neural placode to the diameter of the dural sac on the post-operative axial MRI. The sacs are graded as loose, with ratios less than 30%; moderately loose, with ratios between 30% and 50%; and tight, with ratios greater than 50% (Fig. 36). In our series of 315 total resections reported in 2013, 227 (72%) had loose sacs, 73 (23.2%) had moderately loose sacs, and only 15 (4.8%) had comparatively tighter sacs [61].

Redo lipomas are more likely to harbour visible remainder fat and to have higher cord-sac ratios, likely because the hard, grasping fibrous scar from prior surgery cements the remainder fat to the dura and makes it extremely difficult to detach, and more importantly, the dull gray colour of the cicatrix, unlike bright yellow virgin fat, can be impossible to distinguish from the white plane. The surgeon thus tends to be over-conservative in the dissection and leaves behind a thick layer of stiff scar-infiltrated fat attached to a bulky placode that is well-nigh impossible to neurulate comfortably. The same unyielding fibrous muddle at the DREZ often leads to “gouging”, which may explain the high incidence of post-operative dysesthetic pain in “redo” versus “virgin” patients [59].

Incomplete terminal untethering of the placode predictably ends in early clinical relapse [9,62,74]. In exceptionally large transitional lipomas, the caudal placode is mired in fat, and its complete detachment cannot be done safely without substantial removal of fat. Also, healthy looking nerves are sometimes seen enmeshed in fat distal to what was reckoned to be the tip of the placode, making it seem impossible to achieve terminal disconnection without sacrificing functional cord. Electrical stimulation of these nerves will find them to be non-functional vestigial coccygeal roots. In such cases, 2 to 3 sets of “live” anal sphincter roots should be located on the conus proper above, so that a decisive transection of the vestigial placode below will achieve complete terminal untethering without sacrificing function [58-61].

Our experience unequivocally shows that chaotic lipomas are the most treacherous lesions. Some chaotic lesions are easily recognisable by the presence of obvious ventral fat in between pairs of ventral roots on the MRI, but other less blatant ones have sub-resolution trails of fatty infiltration through some of the DREZ into the ventral motor horns zone, detectable only at surgery (Fig. 26A). Compared to other lipoma types, chaotic lipomas are more likely to show conspicuous residual fat and high cord-sac ratio on the post-operative MRI [59-61] (Fig. 26D). The strategy for these difficult lipomas is learning to resist digging too deep once enough dorsal fat has been removed to enable partial neurulation on the dorsal portion of the lipoma. Since it is never feasible to totally resect the ventral fat or to achieve even clumsy neurulation, its nascent pial surface that had presumably existed without adhesions since birth, should best be kept unabraded so as not to incur iatrogenic tethering (Fig. 26C).

Finally, I disagree with Arai et al. [1], Chapman [8], Chapman and Davis [9], and Kulkarni et al. [27] that “lipomyelomeningocoeles”, or what I call lipoma with extraspinal extension, have higher surgical risk and worse outcome than “regular lipomas”. As long as one recognises and gently handles the extruded part of the neural placode beyond the dorsal plane of the spinal canal, the technical steps of fat resection, placode reconstruction, and dural grafting are identical to those used for the more orthodox lipomas, with comparable results. I also think that Kulkarni et al. [27], and Chapman’s [8] warnings about lipomas in adults being technically more challenging are unwarranted. Except perhaps for thicker “natural” arachnoid bands in adults and more laborious bone and fascial exposure, most of the microsurgical work is the same as for resecting lipomas on young children and infants.

Our rate of new neurological and urological symptoms following total/near-total resection is 4.1% [61], which compares favourably with the 0.6% to 10% (average of 3–7%) in the literature [1,2,10,19-21,25,26,29,37,38,41,63,64,70,73], all pertaining to partial resection presumably using less aggressive techniques than ours. Only 1.5% of our patients had new weakness but 4% had neuropathic pain [59-61], which could be related to mechanical or thermal perturbation near the DREZ from diathermy and gouging. This has taught us to avoid cautery as much as possible and use gentle tamponade and gelfoam. If diathermy is absolutely necessary, we use only the ultra-fine tip irrigating bipolar set at the lowest current intensities, always precisely localizing the bleeding spot using the intermittent squirt-irrigation technique from the bubble-squeezer.

Our rates for CSF leak (0.7%) and wound complications (1.1%) with total resection [61] are much lower than almost all of the published series (of partial resection), which report CSF leak rates from 2% to 47% [10,19,25,26,29,41,63,70,74] and wound dehiscence and infection rates of 2% to 26% [19,22,25,29,41,63,70,74]. The following time-tested technical points concerning wound closure are worth noting : 1) adequate caudal laminectomy is necessary to locate a healthy dural edge at least 5–10 mm past the tip of the neural placode to sustain good suture hold for the lower end of the graft anastomosis, which is always the tenuous end. Ideally, this very edge should be sturdy dura and not fat of the distal lipoma stump. A good caudal dural edge is usually available with dorsal lipoma whose fatty stalk ends rostral to the conus as does the dural defect, but in some very large transitional lipomas, the entire conus is involved in the lipoma and the caudal dural edge can be partly or wholly infiltrated by fibrous fat. The surgeon will have to improvise on finding the best possible suture hold for the lower end of the graft, occasionally resolving to using “big bites” on fibrous fat or through flakes of the incomplete deep fascial layers. Fortunately, this is an uncommon situation. 2) Patience and ingenuity must be used to achieve absolute water-tight closure of the graft with Prolene, followed by Valsalva manoeuvres. 3) We are not as enchanted by synthetic sealants or organic tissue glues for the graft anastomosis as before, for nothing can substitute for solid closure. Use of these agents is optional in cases of tenuous suture line. 4) In large lumbosacral lipomas, gaping muscle and fascial defects may forestall primary approximation of the deep layers at the lower end of the opening. An effective solution is to create generous paramedian relaxing incisions on the flanking lumbodorsal fascia to allow the fascial edges to slide towards the midline and be primarily closed without tension. And 5) the large subcutaneous lipoma is never removed during the initial soft tissue dissection to avoid creating a large dead space that could potentially encourage CSF leakage and formation of a tense pseudomeningocoele. The latter may compress and flatten the dural sac against the placode or even threaten the viability of the skin flap.

The results of total resection is best analysed by comparing its outcome with that of the traditional technique of partial resection. This has proven to be a convenient enterprise for the author, who had performed 116 partial resections prior to 1991, using the same meticulous adherence to technical details as for the total resection series. These comparisons are done in two parts, that of the immediate post-operative results and the long term outcomes of these two different techniques.

The immediate effects of surgery during the first 12 months are very similar between our own total and partial resection groups [59-61]. For asymptomatic patients, the rates for neurological preservation are 98% for total and 94%, for partial resection, respectively. For symptomatic patients who had total resection, 61% had normalisation or improvement, and 33% had stabilisation of neurological status, giving a combined rate of 94% for improvement or stabilisation of disease. Similarly, symptomatic patients who had partial resection had a 33% improvement and 62% stabilization rates, thus also having a 95% rate of short term protection.

When the early post-operative results are compared between our total resection group and partial resection series from the literature [1,10,19,29,41,64,74], it is again apparent that both the disease improvement and stabilization rates are very similar, particularly among patients with progressive symptoms. This suggests that the immediate benefits of surgery in the early post-operative period, for both techniques, are owed to the abrupt interruption of the tethering effect on the cord rather than the amount of lipoma removal or work on the placode. In contrast, surgeons who lamented their inability to completely detach the terminal placode from the lipoma stump in some patients, due to massive caudal fat and undefinable placode-lipoma anatomy, also reported their early recurrence of symptoms [9,63,74].

When the catalogue of pre-operative symptoms are analysed in regards to their response to total resection, the abatement of pain came out the best and most reliable. Typically, the sharp, dysesthetic pain in the lower limbs and perineum will significantly diminish within 3 months [61]. Relief of low back pain, which may be mechanical in origin, is less reliable [18,57]. Children do not usually complain of back pain but they do seem to become more active and playful. Active sensory symptoms such as dysesthesia and hyperpathia also respond favorably with surgery. Although only 20% of patients have actual normalisation of motor deficits, the majority with pre-operative weakness will substantially improve [59-61]. Like tethered cord syndrome in general, recent and milder deficits and symptoms have better chance for good recovery than severe chronic ones. Unlike pain and sensorimotor deficits, bladder dysfunction rarely improves significantly and if so, the recovery is never complete, and partial recovery occurs in no more than 20–30% of patients [59,61]. Amongst the several subtypes of neuropathic bladder, the spastic, small capacity bladder with uninhibited detrusor contractions tends to respond best to surgery. The atonic bladder virtually never improves to a point of not needing permanent intermittent catheterization, and the response of detrusorsphincter dyssynergia is at best partial. It is strongly advisable to obtain formal cystometry and voiding cystourethrogram 3–6 months after surgery and yearly thereafter if indicated to assess whether more radical urologic procedures such as bladder augmentation or ureteral conduits might be needed to eliminate reflux and upper urinary tract infections.

Whilst the immediate benefits of both total and partial resection are due to the equivalent relief of traction on the conus in both procedures and are therefore comparable [59-61], the long term benefits of total over partial surgery probably come from the sustainment of the untethered state when the lipomatous cord underwent aggressive fat removal and protective reconfiguring of the neural structure, an undertaking obviously unobtainable with partial resection. This is made very plain when the progression-free survivals (PFSs) of our own series of total and partial resection are plotted out for a period of 20 and 11 years, respectively. The PFS after total resection for all lipoma types and clinical subgroups is 88.1%, versus 34.6% for partial resection [61] (Fig. 37). The differences in outcome between the two techniques are even more marked if the subgroup PFSs are individually compared, when the patients in each treatment group are segregated by the presence or absence of pre-operative symptoms, age, and whether previous surgery had been done [59-61]. Overall, the risk of symptomatic recurrence is 5.94 times higher with partial resection compared with total/near-total resection over 18 years by the Cox Proportional Hazard Regression Model, with a p-value <0.00001. This striking difference in outcomes between total and partial resection is equally obvious when the results of our total resection group are held up against the published results of partial resection [1,8,11,12,41,63,64,67,68,70,74], especially if the comparisons are done with matched patient profiles (most published series include only virgin cases whereas ours has both virgins and redos) and lesion types (many published series include terminal and filar lipomas which are technically far less complicated and have better prognosis). Barring these and other minor criticisms (e.g., our data are prospective whereas most published series are retrospective), these elaborate comparisons all show far better long term prognosis with total/near total resection, which constitutes the best reason for its endorsement over all other treatment options for complex spinal cord lipomas.

Above all, the most important and certainly most often asked question is undoubtedly whether surgery should be offered to children with asymptomatic lipomas. In 2004, a cohort of 50 children with asymptomatic lipomas were prospectively followed without surgery for 9 years in Paris [27], and were found to have a deterioration risk of 33% with a PFS probability of 67% [27]. A retrospective study from London, with similar patient numbers (56 children) and profiles also reported a 10 years disease progression rate of 40% and PFS of only 60% with non-surgical treatment [73]. The London study also found that the female gender, transitional lipomas, and conus syringes are all associated with a higher rate of deterioration which also occurs earlier than patients not having these traits. Since transitional lesions and females are usually more numerous in most lipoma cohorts, as are conus syringes, one could surmise that there is a large subclass of children with these traits who will have a worse than 40% prospect of disease progression [48] (Fig. 45). Given that children within the lipoma age range have an actuarial life span of 65 to 70 years, and that established neurogenic bladder and motor weakness seldom fully recover following post factum salvage surgery [2,6,29,41,70,74], the push for preemptive surgery for asymptomatic lipomas would seem logical if it can be shown to offer clear-cut outcome advantage over non-surgical management.

Total resection, as is amply shown here, does just that. When the subgroup of 113 asymptomatic children with virgin lipoma from our total resection cohort is put up against the Paris and London groups, the superiority of total resection is obvious, with a 20 years PFS of 98.8% [61] compared to the 10 years rates of 67% and 60% for conservative management in Paris and London, respectively [27,72] (Fig. 46). In addition, our total resection PFS curve shows disease stabilisation 5 years after surgery, whereas there is probably continued disease progression beyond 9 or 10 years with no surgery [27,73]. There is thus strong statistical support for endorsing total resection, not only for symptomatic children but also as prophylactic treatment for asymptomatic children with lipomas, at least those with the dorsal and transitional types (see below for chaotic lipomas).

There are currently no data on the rate or probability of disease progression for adults with asymptomatic lipomas, and their actuarial life span is obviously shorter than that of children, so the cumulative risk for adults should be far smaller. A forceful argument therefore cannot be made for prophylactic surgery in asymptomatic adults, but when a lipoma becomes symptomatic, further deterioration is usually inevitable, and aggressive resection can then be justified for both children and adults.

My firm answer to this question is a definitive yes. To start, the 11 years PFS probability of 34.6% from our own partial resection series of 116 lipomas [59-61] is clearly inferior to the Paris (PFS of 67%) and London (PFS of 60%) series [27,73] of observation alone. If we now calculate outcome only on our asymptomatic virgin cases who had partial resection to match the profiles of the other two series, in essence eliminating the fastidious redo lipomas, their 11-year PFS after partial surgery is only 43% [60], still far short of the Paris and London numbers [27,61,74]. Moreover, the Parisian series of partial resection [27] managed only a slightly higher PFS of 51% (Fig. 46), and other similar series report equally dismal or worse PFSs, far worse than no surgery. Minus the good-risk terminal lipomas, Colak et al.’s series [11] would have a less than 50% PFS, as would Pierre-Kahn’s partial resection series a less than 40% PFS [63]. Cochrane et al.’s [10] partial resection of transitional lipomas had a 10-year PFS of only 20%, and Cornette et al. [12] conceded unaltered progression of disease after partial resection.

The explanation for the above statistics is starkly obvious if one had the unpleasant experience of exploring lipomas that had undergone partial resection, as I did more than 150 times, and witnessed how the grotesquely contorted, heavily fat-endowed, and unneurulated placode could be solidly welded to the dura by rigid scar far worse than in an unoperated lipoma with its nascent surface. If the frequency and speed of symptomatic recurrence are proportional to the extent and firmness of fixity of the placode, one would certainly expect partial resection to incur quicker and more severe functional impairment than if no surgery had been done, which is clearly shown in our 2013 analysis [61]. The time course of in situ scar formation also explains why partial resection typically gives vimmediate clinical improvement owing to the initial relief of tethering but is unable to sustain these short-lived benefits against the slow but inexorable reality of chronic progressive scar formation, ending in an unrelenting downhill path that is clearly worse than the natural history of the disease.

Our extensive literature search suggests that the current global practice of lipoma surgery comprises a continuum of techniques ranging from perfunctory whittling of fat without placode refurbishment, to complete resection of lipoma, elaborate reconstruction of the placode, and capacious dural grafting, as is endorsed here. In between these two extremes, there is at least one historical series that describes the half-measure of “subtotal fat removal” and “partial neurulation”, and reports somewhat better results than non-surgical treatment [29]. The thoroughness of “clean” placode reconstruction, which is estimable by MRI, thus appears to be commensurate with the clinical benefits, and that the projected outcome of non-surgical treatment lies somewhere between the two extremes of skimpy and complete fat removal. This would also imply that partial resection will in the long run prove more harmful than no surgery for the patient. In this context, I rather strongly think that partial resection should be discouraged.

Since our 2013 report [61], the ever-enlarging data pool on total resection has induced the author to consolidate a few recommendations regarding treatment that were, at best, tentatively entertained before.

According to our total resection data, the type of lipoma should not affect outcome projection [60,61], but in reality it probably does. One of the limitations of biostatistics is its inherent fallacy of rigidly assigning finite variables to represent the almost infinite vicissitudes of biological forms. For example, under the same umbrella of transitional lipomas, there are lesions with relatively orderly alignment of DREZ and nerve roots, a predictable lipoma-cord interface, and manageable quantities of fat, and there are also lipomas with plume-like billows of smothering fat that defy designation. The success and complication rates for these two extremes cannot be the same, and indiscriminately blending their divergent statistical weights is accordingly misleading. Thus, the blanket statement of “no statistical difference” in outcome between lipoma types should not be taken too literally, nor should it supplant an experienced surgeon’s impression, despite comforting statistics, that some sprawling, intractable transitional lipomas demand much more exacting skill and portend a graver prognosis than a tamer, friendlier dorsal lipoma.

By far the most difficult and treacherous lipomas I have ever tackled are the chaotic lesions. The demarcation between fat and neural tissue is sometimes indiscernible even within the dorsal portion of these lipomas, and the resection should be more conservative and aim only to remove just enough dorsal fat to enable a comfortable neurulation of the dorsal part. I have repeatedly emphasised restraint and avoid doing damage to the pia covering the ventral fat since its complete resection and ventral neurulation are never possible. Consequently, it is not uncommon for chaotic lipomas to have higher cord-sac ratios and display more residual fat than the other two lipoma types on the post-operative MRI (Fig. 26D).

When in 2010 we compared the total resection outcomes of the three lipoma types in a cohort of 238 patients, we found no actual statistical differences between them [60]. However, even with the caveat of small sample size of only 10 chaotic lesions, the PFS curve for chaotic lipomas ran considerably lower than the curves for dorsal and transitional lesions, and the p values between chaotic and the other two lesions were only very slightly higher than 0.05, giving us the preliminary suspicion that chaotic lipomas had worse prognosis than the others. In our 2013 series of 315 total resections [61], the number of chaotic lipomas has risen to 28. The PFSs for dorsal and transitional lipomas of 92.2% and 86%, respectively, remained very similar to the 2010 figures, again without statistical difference with a p-value of 0.458. However, the PFS for chaotic lesions has dropped to 54% and its regression curve separates even further away from the other two curves than in 2010 (Fig. 47). Within this chaotic group, there were no patients with cordsac ratios lower than 30%, and their post-operative MRI often showed a hefty placode with a loathsome amount of remainder ventral fat and a tight container fit [61]. Mathematically, the outcome differences between chaotic and the other 2 lipoma types only barely reach statistical significance (p-value of 0.0492 with dorsal lipoma and 0.0481 with transitional lipoma) but given larger numbers in the future, the rank of chaotic lesions might very well be definitively downgraded to the most sinister of the three lipoma types.

In Fig. 47, I inserted the London outcome curve of non-surgical treatment on to the PFSs of the 3 lipoma types. The 54% PFS of chaotic lipomas, after aggressive resection, is actually worse than both the London and Paris series of non-surgical treatment, which begs the question whether asymptomatic chaotic lipomas should be treated with any prophylactic surgery, regardless of technique. This sobering observation has changed my 2010 stance of prophylactically resecting all types of asymptomatic lipomas, and I now recommend that asymptomatic chaotic lesions, if unmistakably diagnosed on MRI, should be closely observed without surgery until symptoms develop.

For all the lofty statistics and extravagant analyses, there remains the unanswered question whether symptomatic lipomas do worse than asymptomatic ones after total resection. In our 2013 series of 315 patients [61], multivariate analysis finds no statistical difference in outcome between symptomatic and asymptomatic lesions, but univariate analysis, in contrast, shows that asymptomatic lesions had significantly better outcome than symptomatic lesions, as we have found in our earlier series of 238 patients (Fig. 48). Even when the analysis is run just on the virgin lesions to eliminate the “redo factor” among symptomatic patients, asymptomatic patients still came out much better [60] (Fig. 49).

Besides our own results, several large series in the literature [16,29,63] also report considerably better outcome for asymptomatic than symptomatic patients. It was once argued that children with symptoms tend to be older and are thus more likely to undergo growth spurts and take up rigorous sports, both situations subject the spinal cord to pernicious tugging known to trigger symptoms in any tethered cord conditions, whereas asymptomatic children are much younger. The postresection profiles of the two groups are thus not comparable as the symptomatic older child is being followed at a more vulnerable age [29]. Whilst this may explain some cases of early recurrence in the symptomatic group, Byrne et al.’s series of 100 infants, which eliminated the age difference in the two groups, still shows a markedly better outcome for asymptomatic infants [6]. Current consensus seems to support the notion that there are indeed prognostic differences between symptomatic and asymptomatic lipomas.

To date, no consistent dissimilarity in size, architecture, or histology has been found between symptomatic and asymptomatic lipomas, but there may be invisible differences in susceptibility inherent within their respective spinal cords. Perhaps the already injured cord that is showing symptoms has become more “fragile” and possesses a lower threshold for new symptoms with even “slight” retethering. Perhaps those spinal cords which develop early symptoms are also intrinsically predisposed to sustain new injuries to even minor future insults and are thus destined to have earlier disease recurrence.

Total/near-total resection of complex spinal cord lipomas and complete reconstruction of the neural placode produce a much better long term symptom-free survival than partial resection. Partial resection causes new and exuberant adhesions between the cut surface of the remainder fat and dura, resulting in earlier and firmer retethering and consequently a worse prognosis compared to no surgery. Our post-operative neurourological and wound complications for total resection are either comparable to, or lower than, most series of partial resection.

Total resection also confers much greater long term benefits than no surgery in children with asymptomatic virgin lipomas. The ideal patient profile for total resection predictive of early disease stabilisation and the longest recurrence-free survival is that of a child less than 2 years old who is without symptoms or prior surgery. We therefore strongly recommend prophylactic total resection for asymptomatic dorsal and transitional lipomas in children. Multivariate analysis also shows that a low post-operative cord-sac ratio is highly predictive of good long-term outcome. My firm impression is that a well-executed neurulation is just as important in preventing retethering.

Our experience so far shows that chaotic lipomas are the most treacherous, and the majority are simply not amenable to thorough resection or optimal placode reconstruction, let alone attaining the goal of a low cord-sac ratio. Their poor statistics are unlikely to improve even with larger numbers, and consequently I do not recommend prophylactic surgery for asymptomatic chaotic lipomas, a rather drastic change from our 2013 endorsement.

A lengthy analysis like this one is futile unless it can provide at least a few serviceable “truths”. Contrary to the skewed opinion of those who had not actually seen the operation, the technical aspectsof total resection can be learned by any willing neurosurgeon with a modicum of patience, tenacity, and open-mindedness. Those who have observed the surgery will attest that other than a few unaccustomed manoeuvres and tricks, which can be learned, the rest is strictly standard microsurgery. The intraoperative electrophysiology part can be managed by any trained neurophysiologist, and the equipment should be purchasable at reasonable cost.

Last but by no means least, our massive outcome data collected over 25 years powerfully endorse total resection for asymptomatic dorsal and transitional lipomas in children and for all symptomatic lipomas in all ages. The timing of surgery for children should be soon after diagnosis, except in very young infants with stable neurology, for whom surgery is delayed till 6 to 12 months of age to minimise surgical and anaesthetic morbidity. Surgery for asymptomatic chaotic lipomas is withheld until symptoms develop.